RuntimeError: An attempt has been made to start a new process before the current process has finised

一、问题描述：
在运行下面代码时出现RuntimeError: An attempt has been made to start a new process before the current process has finished its bootstrapping phase.

# TODO 进程池的使用
from multiprocessing import Pool
import os, time, random

def worker(msg):
    t_start = time.time()
    print("%s开始执行,进程号为%d" % (msg,os.getpid()))
    # random.random()随机生成0~1之间的浮点数
    time.sleep(random.random()*2) 
    t_stop = time.time()
    print(msg,"执行完毕，耗时%0.2f" % (t_stop-t_start))

# 定义一个进程池，最大进程数3
p = Pool(3)  
for i in range(0,10):
	# Pool().apply_async(要调用的目标,(传递给目标的参数元祖,))
	# 每次循环将会用空闲出来的子进程去调用目标
	p.apply_async(worker,(i,))

print("----start----")
p.close()  # 关闭进程池，关闭后po不再接收新的请求
p.join()  # 等待po中所有子进程执行完成，必须放在close语句之后
print("-----end-----")	

运行结果：

二、解决方法:
通过main方法来执行python文件，代码如下

# TODO 进程池的使用
from multiprocessing import Pool
import os, time, random

def worker(msg):
    t_start = time.time()
    print("%s开始执行,进程号为%d" % (msg,os.getpid()))
    # random.random()随机生成0~1之间的浮点数
    time.sleep(random.random()*2) 
    t_stop = time.time()
    print(msg,"执行完毕，耗时%0.2f" % (t_stop-t_start))

def main():
	# 定义一个进程池，最大进程数3
	p = Pool(3)  
	for i in range(0,10):
		# Pool().apply_async(要调用的目标,(传递给目标的参数元祖,))
		# 每次循环将会用空闲出来的子进程去调用目标
		p.apply_async(worker,(i,))

	print("----start----")
	p.close()  # 关闭进程池，关闭后po不再接收新的请求
	p.join()  # 等待po中所有子进程执行完成，必须放在close语句之后
	print("-----end-----")

if __name__ == '__main__':
	main()

运行结果：
We read the world wrong and say that it deceives us.